Concrete walls and other concrete structures, have traditionally been made by building a form. The forms were usually made from plywood and other wood members. Unhardened concrete is poured into the form space provided in the form. Once the concrete hardens, the form walls are removed leaving a concrete wall or other concrete structure/structural member.
Given the limitations in structural strength of concrete when subjected to certain types of loading such as tensile loading, it is known to provide reinforcement for the concrete. The reinforcement is typically accomplished by placing metal reinforcement bars (usually made from steel) within the space defined by the form. The precise positioning of the reinforcement bars is important and is selected to maximize the structural benefit and at the same time ensure other design criteria are met (e.g. ensuring a sufficient amount of concrete coverage for fire protection). After the reinforcement members are properly positioned, concrete is poured into the form space covering the steel reinforcement. The concrete is then allowed to harden, bonding the concrete to the steel reinforcement. The bonding between reinforcement and concrete is typically enhanced by providing reinforcement members that have ribbed outer surfaces. The overall composite structural member has enhanced load-bearing capacity and provides the possibility of being able to optimize the concrete structure thickness, and consequently economize on the materials and expenses for building erection.
The task of properly placing and positioning the reinforcement members within the form space however can be problematic. The reinforcement members are typically long steel rods. These rods must be supported if they are to be properly and securely positioned in the form space. Accordingly, systems have been developed to ensure that the reinforcement members are properly positioned within the form space and remain in their desired orientation and position throughout the concrete forming process.
One technique has been to form a cage of reinforcement members wherein larger reinforcement rods are bound together with binding wire. Building such a cage inside of a constructed form space is quite difficult and time consuming. One alternative is that the reinforcement cage can be constructed outside the form space and then lowered into the form space. However, for large structural members, this is often difficult given the large weight of the cage structure. Another possibility is that the cage can be first built and then the form constructed around the reinforcement cage.
These known methods require special devices for installation of the ribbed rods into the form space of the erected concrete structure, as well as a large amount of time to control the correctness of the reinforcement cage position.
Additionally, these known techniques are generally quite time consuming and costly due to the fact that additional steel material is consumed for the purpose of improving the bearing capacity of the concrete structure protection, to compensate for a failure to ensure high accuracy in the positioning of the ribbed rods. Therefore improvements in the method of placement of the reinforcement within a form space are desirable.
U.S. Pat. No. 6,216,412 to Offersen is directed to the reinforcement of a concrete structure that employs an assembly frame having pairs of transverse and longitudinal girders. Cut outs are provided in the outer sides of the assembly frame. The cut outs receive one or more reinforcements rods which are held in position in the cut outs by spring shackles. Additional reinforcement rods are provided oriented transverse to the first rods in the cut outs, and are held in place relative to the first rods in the cut outs by spring shackles. Although providing some improvements in the reinforcement of concrete, Offersen still requires the use of a fairly complex structure and method to create the necessary reinforcement.
Aside from providing improvements in the positioning of reinforcement in the forms, there is generally a need to improve overall concrete forming systems. Known improvements include improvements in the materials used in building the form walls that define the form space, and in the methods of constructing forms. For example, techniques have been developed whereby concrete walls are formed using modular panel components that can be interconnected to build the form. In some known form systems, the modular panels are made from a foam or plastic insulating material. The foam panels can remain in place after the concrete hardens as a permanent part of the building, providing such benefits as sound and heat insulation.
In such systems the panels can be interconnected as desired to provide an appropriate shaped and sized concrete wall.
In order to assist in keeping the modular panel walls properly spaced when concrete is poured between the form walls, transverse tie members are used in order to prevent transverse displacement of the walls due to the hydrostatic pressure created by the unhardened concrete. However, the incorporation of tie members into the overall form structure provides further complication and additional materials.
U.S. Pat. No. 5,887,401 issued to Moore Jr. on Mar. 30, 1999 discloses a concrete form system comprising two longitudinally-extending side panels with connectors contained in the body of the panels. The panels are spaced by means of horizontal wire meshes. The meshes are connected with said connectors. Each connector has a support portion, which receives the hydrostatic pressure of unhardened concrete, and a portion, which connects to the mesh. Despite the fact that this system reduces material consumption in concrete structure forming and in longitudinal reinforcing, it requires additional components, material and time for vertical reinforcement. Additionally, the locking connection of the panels with the horizontal meshes presumes building of the form only at the construction site due to the fact that they do not properly stabilize the panels used for forming during transportation from the plant to the construction site. The connection is only blocks the panels from transverse movement, but does not have the capability of being tightened these panels. Besides, installation of vertical reinforcement at the construction site is quite labor intensive.
U.S. Pat. No. 5,809,725 issued to Pierro Cretti on Sep. 22, 1998 discloses A concrete form system made from polystyrene boards, connected at a distance from each other by a prefabricated nog structure comprising plastic inserts with screw-type side surfaces and inside blind openings connected to the threaded end of a tie rod made of steel. In the plant environment or on the construction site, vertical and horizontal rods for reinforcement of concrete structure are fixed to tie-rods. Also, the invention presumes the combined installation of the reinforcement rods, namely, a part of vertical rods are fixed to the tie rods at the plant, and horizontal rods are installed on the construction site right before concrete pouring by means of installation via eyes made in the tie rods. This system solves the problem of the “air bridge” and presumes delivery of the panels together with vertical reinforcement to the construction site.
However, manufacturing of the formwork by means of connection of three elements with different strength by screwing of screw-shaped hollow insert from thermoplastic into the polystyrene board, and simultaneous screwing of the insert cavity onto the thread of the steel rod is very problematic. The result is typically damage to the less strong element, the polystyrene board's body. Consequently, such connection will have low bearing capacity for receiving hydrostatic pressure of the newly poured concrete and require increasing the width of polystyrene board or geometrical sizes of the insert, which increases the cost.
Also, it is necessary to note, that the installation separate vertical rods and fixing them to steel tie rods even at the plant is very labor consuming. Special equipment and a lot of time are required to control the proper installation of the reinforcement in the space of the formwork. Additionally, the manufacturing and proper installation of the tie rods with eyes for positioning of the horizontal reinforcement on the construction site is relatively complicated and relatively expensive.
U.S. Pat. No. 6,176,059 to Cantarano et al. discloses a modular construction system which uses modular wall panels, connectors and structural tie plates. In this system, the tie plates are elaborately formed with a series of integrally formed openings and clamps, which serve to lock in place both horizontal and vertical reinforcement bars. This system is, however, relatively complicated and would be relatively expensive to implement. Furthermore, providing these tie plates would likely create structural deficiencies and would in most cases not satisfy most building codes.
Accordingly, improved systems and methods for providing reinforcement of concrete structures are desired, as are improvements in the overall form systems used to make concrete structures that incorporate reinforcement.